1. Field of the Invention
The present invention relates to a process to form a semiconductor laser diode (LD), in particular, to form an LD implementing with a sampled grating.
2. Related Background Arts
A wavelength tunable LD usually provides an optical grating, especially, a sampled grating to tune an emission wavelength thereof, where the optical grating is often provided under an active layer, or a waveguide layer. A sampled grating has a structure with a number of grating regions formed at a constant interval, and each of the grating regions includes a number of gratings each having refractive index thereof different for those of neighbor regions. However, when the number of the gratings in one grating region, or when the gratings have physical shapes off from the desired one, such a sampled grating may show optical performance different from the designed one, or degraded from those of desired performance.